Nanowires are intended to be used for several applications within integrated circuits. One of the most important among these applications is the manufacturing of MOS transistors with channels composed of nanowires. Such transistors do not exhibit the so-called short channel effect and consequently provide for better control of the electrical conduction of the channel. Other applications for nanowires include the manufacturing of electrically conducting connections, resistors with resistance values controlled via the diameter of the resistive portion, stretch-sensors, etc.
At least three processes have already been implemented for manufacturing nanowires.
According to a first one of these processes, a stack comprising a layer of silicon superposed on a layer of silica is formed on a substrate of an integrated electronic circuit. Then the layer of silicon is etched from the top surface of the circuit in side parts of the stack so as to form a silicon track. Then, the silica material is selectively etched under a center portion of the track, so that a gap appears between this center portion of the silicon track and the substrate beneath. Afterwards the circuit is heated so as to make the cross-section of the center portion of the silicon track round. The silicon material is oxidized at the surface of the track and the silica material thus formed is selectively etched. Oxidizing and etching steps are alternately repeated so as to reduce progressively the diameter of the track in the center portion.
A second process involves a stack structure including hard masks. One of the hard masks has an opening with two opposite edges that are apart from each other with a separation gap smaller than opposite edges of an underlying silicon layer portion. The silicon layer portion is etched through the mask opening, thereby producing two parallel silicon wires along the edges of the mask.
Finally, a third process consists in growing ex-situ nanowires on a seed surface of silicon or germanium which supports nanoparticles of a catalyst, for example nanoparticles of gold. When such system is heated so that each catalyst particle forms a droplet on the seed surface, and further is fed with a gaseous precursor of silicon or germanium, then a nanowire grows from each catalyst nanoparticle with the longitudinal direction of said nanowire oriented perpendicular to the seed surface. Once a nanowire has reached a desired length, it is brought to the desired location on a circuit substrate. Handling of the nanowire from the growth location to the final location on the substrate can be performed using a tip similar to that of an atomic force microscope. But it is difficult to form a nanowire quite long using such process, and the shape of the nanowire portion is not well-controlled.
All processes cited above comprise many processing steps. Therefore, processing time of an integrated circuit which incorporates a nanowire so-obtained is long, leading to a high production cost.
Thus, there is a need to produce an integrated electrical circuit with at least one nanowire in a practical manner, with reduced increase in the production cost of the circuit.